This invention relates to offshore oil production apparatus and, in particular, to tieback tools for connection of a tieback conductor to a subsea well.
Offshore oil wells may be drilled from a drilling vessel or rig and thereafter produced to a fixed platform. Typically, once a well is drilled to depth, it is plugged, a protective cap installed and the drilling vessel moved to another well location. The fixed platform is then moved to a position over the well, the cap removed and tieback conductors are run from the platform deck to the well. Tubing is then run, surface production trees installed, and the well produced in the conventional manner.
A complication comes about, however, because it is nearly impossible to align the fixed platform precisely over the well system and, although the tieback conductor string runs through the guides at various elevation, offset still occurs due to well system settling and other physical factors. The problem of misalignment is particularly acute in the vicinity of the well system where the tieback conductor is to be joined to the well.
Funnels have been used in tieback tools or connectors as one way to overcome the alignment problem and to prevent damage to engaging threads as shown, for example, in U.S. Pat. Nos. 4,343,495 and 4,408,782. These funnels align the tool with the well system before threading the tool onto the well system. Another way to solve the problem of misalignment is to use either a tieback tool, such as shown in the co-pending application of Hughes and Milberger, application Ser. No. 659,603 entitled Misalignment Tieback Tool--Rotating Casing, filed 10/12/84, or such as shown in the co-pending application of Hughes, Ser. No. 659,605, filed 10/12/84 entitled Misalignment Tieback Tool--Non-Rotating Casing. The Hughes and Milberger tieback tool has a threaded ring with dogs for aligning with J-slots in a casing hanger for initial alignment. After this initial alignment, continued rotation of this tieback conductor actuates the threaded ring to lock the tieback tool onto the casing hanger via the dogs and J-slots. (In the Hughes invention, the dogs, although on the body of the tool, cooperate similarly with J-slots in a casing hanger, but a torquing tool is used to rotate a threaded ring to lock the tieback tool to the casing hanger.) The tieback tool of the Hughes and Milberger application is characterized by a rotation of the tieback conductor to lock the tieback tool into the well system, whereas the tieback tool of the Hughes application does not require rotation of the tieback conductor, but uses a torquing tool to lock the tieback tool into the well system.